What was the ambient temp when you ran your test?
To clear up a misnomer, the thermostatic plate does not open at 180F but rather it closes the bypass opening that allows the oil to flow directly back into the engine. The cooler is always flowing oil but 100% of the oil does not go through the cooler until 180F.
I have half my 25 row blocked off for street driving and have yet to see more than 195F. Cooler mornings <60F the oil is slow to warm and will hover between 170-180F.
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